1. Field of the Invention
The present invention relates to a wire harness.
2. Description of the Related Art
Conventionally, when wireless communication has been used inside vehicles, such as automobiles, reception strength has been reported to largely vary due to multiple reflection of narrow band signals in the vehicles. Thus, for example, as disclosed by T. Kobayashi in “Measurements and Characterization of Ultra Wideband Propagation Channels in a Passenger-Car Compartment”, IEICE Trans. Fundamentals, pp. 3089-3094, Vol. E89-A, No. 11, November 2006 (hereinafter, “Non-Patent Literature 1”), variation in reception strength is restrained by use of the ultra wideband (UWB) technique, which uses ultra wideband radio.
However, since the method described in the above mentioned Non-Patent Literature 1 uses a wide band, in terms of frequency utilization efficiency, the method is considered to be socially undesirable. For example, with the method described in Non-Patent Literature 1, problems related to electromagnetic compatibility (EMC) and interference are difficult to be cleared, and the method may be unable to be utilized under the current Radio Law. Further, in the method described in Non-Patent Literature 1, since ultra wideband signals are handled, the problem that the load on the transmitting and receiving device is large and the electric current consumed is increased is not negligible. Accordingly, the method described in Non-Patent Literature 1 adopting wideband wireless communication is able to realize restraining in reception strength variation of wireless communication signals in a closed space such as inside of a vehicle, but still has room for further improvement in terms of improving communication quality.
Therefore, in recent years, for use of wireless communication inside a vehicle, such as an automobile, a technique, which restrains reception strength variation of wireless communication signals and improves communication quality, while adopting narrowband wireless communication instead of wideband wireless communication, has been demanded.
As to this demand, as described below with reference to FIG. 5 to FIG. 7, restraining the reception strength variation of wireless communication signals and improving the communication quality by utilization of various types of diversity in narrowband wireless communication may be considered. Diversity herein refers to a technique for improving quality or reliability of communication by, for the same radio signals received through plural antennas, preferentially using a signal of an antenna with better radio wave conditions, or combining the received signals and removing noise therefrom.
For example, as illustrated in FIG. 5, when a space diversity scheme is adopted and a wireless terminal 10 equipped with two antennas (an antenna A1 and an antenna A2 in FIG. 5) is used, a minimum of reception strength is able to be avoided by the use of plural antennas. Further, the space diversity effect is effective when an interval L between the two antennas A1 and A2 is made equal to or longer than “0.3λ”. Herein, λ means a wavelength at a used frequency “f”. When the used frequency “f” is expressed in “MHz”, “λ=300/f [m]”. Thus, if, for example, “1 GHz” is used, “0.3λ” equals about “15 cm”. When a size of the wireless terminal 10 is “15 cm”, the space diversity scheme may be adopted, but when the wireless terminal 10 is downsized to a size less than “15 cm”, the space diversity scheme is unable to be adopted.
Further, as illustrated in FIG. 6, when a polarization diversity scheme is adopted and a wireless terminal 10 equipped with antennas A1 and A2 of two types is used, the antenna A1 is able to be caused to function as a vertical polarization antenna, and the antenna A2 is able to be caused to function as a horizontal polarization antenna. Accordingly, since reflection properties are different between horizontal polarization and vertical polarization, in the wireless terminal 10 of FIG. 6, by using together the antennas A1 and A2 of the two types, the horizontal polarization and the vertical polarization, a minimum of reception strength is able to be avoided. However, in the example in FIG. 6 also, since the wireless terminal 10 needs to be equipped with the antennas A1 and A2 of the two types, the wireless terminal 10 itself is difficult to be downsized.
Moreover, as illustrated in FIG. 7, when a pass diversity scheme or a directional diversity scheme is adopted and a wireless terminal 10 equipped with adaptive array antennas A1 to A4 is used, a minimum of reception strength is able to be avoided. In the example of FIG. 7 also, like the example illustrated in FIG. 5, making intervals L between the respective antennas A1 to A4 equal to or longer than “0.3λ” is effective. In this example of FIG. 7, a multi-input multi-output (MIMO) or space division multiple access (SDMA) system, which is diversity combined with the idea of the adaptive array antennas, is able to be realized. However, in the example of FIG. 7 also, since the wireless terminal 10 needs to be equipped with the respective antennas A1 to A4 forming the adaptive array antennas, the wireless terminal 10 itself is difficult to be downsized.
As described above, in the examples illustrated in FIG. 5 to FIG. 7, by utilizing various types of diversity in narrowband wireless communication, the reception strength variation of wireless communication signals is able to be restrained and the communication quality is able to be improved, but there is room for further improvement for the wireless terminals becoming comparatively large-sized.